The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to deposit and etch film on substrates such as semiconductor wafers. During processing, dummy structures may be used during some processing steps and then later removed during subsequent processing steps. Pure silicon may be used for the dummy structures. For example only, silicon dummy structures may be used as dummy gates for high-k metal gate technology, mandrels for spacer formation and liners for back end of line (BEoL) air gaps.
The dummy silicon structures need to be removed without damaging other structures that need to remain on the substrate. As a result, the etch process to remove the silicon dummy structures should have infinite selectivity to silicon dioxide (SiO2) and/or silicon nitride (Si3N4). Conventionally, wet etching is selected for its superior selectivity performance. However, wet etching may leave residue. As feature scaling continues, silicon residue removal in small spaces is becoming more challenging.
Molecular oxygen (O2)-rich hydrogen bromide (HBr)/O2 plasmas or silicon tetrachloride (SiCl4)-additive plasmas may be used to remove dummy silicon when infinite selectivity to SiO2 and/or Si3N4 is required. Due to excess byproduct (SiOBrx or SiOClx) deposition on the substrate, a diluted hydrofluoric (HF) acid dip is usually required after plasma treatment for post-etch wafer clean. However, the diluted HF acid wet clean process often leads to additional damage to the SiO2 layer.